Accurate IndexOB and IndexMA passes
You will have to render without DOF, and add it in during compositing in order to get clean IndexOB masks. Otherwise you'll probably have to separate via layers if you want in-camera DOF.

Alternatively, you could try this solution, which creates a second Scene, linked to your main scene with the camera DOF turned off. That way your second scene would have IndexOB masks with clean edges, and you can work with both scenes in the compositor. Would that solve your issue? 

I'd be interested to know your final pipeline, I'm dubious that the clean masks would help you modify your DOF renders, but I would be interested to see more about it if it can.